www.impactjournals.com/oncotarget/ Oncotarget, Vol. 5, No. 6 Thermoregulatory correlates of nausea in rats and musk shrews Sukonthar Ngampramuan1, Matteo Cerri2, Flavia Del Vecchio2, Joshua J. Corrigan3, Amornrat Kamphee1, Alexander S. Dragic3, John A. Rudd4, Andrej A. Romanovsky3, and Eugene Nalivaiko5 1 Research Center for Neuroscience and Institute of Molecular Bioscience, Mahidol University, Bangkok, Thailand; 2 Department of Biomedical and Motor Sciences, University of Bologna, Bologna, Italy; 3 FeverLab, Trauma Research, St. Joseph’s Hospital and Medical Center, Phoenix, AZ, USA; 4 School of Biomedical Sciences, Chinese University of Hong Kong, Hong Kong, China; 5 School of Biomedical Sciences and Pharmacy, University of Newcastle, Newcastle, NSW, Australia. Correspondence to: Eugene Nalivaiko, email: [email protected] Correspondence to: Andrej A. Romanovsky, email: [email protected] Keywords: nausea, chemotherapy, temperature, hypothermia. Received: December 21, 2013 Accepted: February 21, 2014 Published: February 22 2014 This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. ABSTRACT: Nausea is a prominent symptom and major cause of complaint for patients receiving anticancer chemo- or radiation therapy. The arsenal of anti-nausea drugs is limited, and their efficacy is questionable. Currently, the development of new compounds with anti-nausea activity is hampered by the lack of physiological correlates of nausea. Physiological correlates are needed because common laboratory rodents lack the vomiting reflex. Furthermore, nausea does not always lead to vomiting. Here, we report the results of studies conducted in four research centers to investigate whether nausea is associated with any specific thermoregulatory symptoms. Two species were studied: the laboratory rat, which has no vomiting reflex, and the house musk shrew (Suncus murinus), which does have a vomiting reflex. In rats, motion sickness was induced by rotating them in their individual cages in the horizontal plane (0.75 Hz, 40 min) and confirmed by reduced food consumption at the onset of dark (active) phase. In 100% of rats tested at three centers, post- rotational sickness was associated with marked (~1.5°C) hypothermia, which was associated with a short-lasting tail-skin vasodilation (skin temperature increased by ~4°C). Pretreatment with ondansetron, a serotonin 5-HT3 receptor antagonist, which is used to treat nausea in patients in chemo- or radiation therapy, attenuated hypothermia by ~30%. In shrews, motion sickness was induced by a cyclical back- and-forth motion (4 cm, 1 Hz, 15 min) and confirmed by the presence of retching and vomiting. In this model, sickness was also accompanied by marked hypothermia (~2°C). Like in rats, the hypothermic response was preceded by transient tail-skin vasodilation. In conclusion, motion sickness is accompanied by hypothermia that involves both autonomic and thermoeffector mechanisms: tail-skin vasodilation and possibly reduction of the interscapular brown adipose tissue activity. These thermoregulatory symptoms may serve as physiological correlates of nausea. INTRODUCTION either due to cancer itself or secondary to chemotherapy [1]. Many commonly used chemotherapeutic agents Approximately half of cancer patients experience (eg. cyclophosphamide and cisplatin) possess potent nausea and vomiting during the course of their disease, emetogenic properties [2]. Nausea and vomiting produced www.impactjournals.com/oncotarget 1565 Oncotarget by these and other chemothrerapeutic drugs are among the in experimental animals, and we have designed our most severe and feared collateral effects of chemotherapy experiments to elucidate this question. Neither subjective [3, 4]. These side effects not only dramatically worsen perceptions nor sweating can be assessed in conscious quality of life, but may affect the patients’ willingness to rodents. On the other hand, core body temperature, continue their anti-cancer treatment. Of interest, nausea cutaneous temperature, and the preference for ambient has a stronger negative impact on patients’ daily life than temperature are readily measurable, but none have ever vomiting [5]. been used in preclinical studies of nausea. Our principal The introduction of the 5-HT3 and neurokinin-1 hypothesis was that pro-emetic stimulation causes (NK1) antagonists substantially improved the management hypothermia and alters behavioral preference for the of chemotherapy-induced vomiting [2, 4]. However, ambient temperature in rodents. paradoxically, their effect on nausea was comparatively modest [6, 7], and it is now becoming recognized that RESULTS nausea and vomiting represent totally different entities, both from the point of view of their pathophysiology and pharmacotherapy [8, 9]. The relative potencies of Provocative motion reduced food consumption in anti-emetic drugs to differentially reduce nausea and rats. emesis were not immediately recognized as nausea was only a secondary end-point in most clinical studies. Likewise, most recent pre-clinical studies of novel anti- Provocative motion had substantial and significant emetic substances are based on emetic responses, and it anorexic effect (Fig. 1): during 30-min test period, rats is assumed that drugs which suppress retching/vomiting subjected to rotation consumed 42% less food compared to in animals may be equally good in suppressing nausea controls (1.4±0.1 vs. 2.5±0.3g, respectively; p<0.05); this in humans. As noted, this is not the case. The situation effect was even larger (49%, or 0.43±0.02 vs. 0.84±0.05 g, is even more complicated in ‘nausea’ studies performed respectively; p<0.05) if food consumption was assessed as in common laboratory animals such as rats and mice, a percentage of increase in body weight. In contrast, there as these animal do not have emetic reflex. Here, a was no effect of rotation on water consumption (2.6±0.3 researcher’s choice for assessing nausea is limited to vs. 2.7±0.3, or 0.85±0.03 vs. 0.85±0.05%, respectively; just a few biological indices with either poor temporal p>0.05 for both). resolution (e.g. reduced locomotion or food intake) or questionable face validity (e.g. pica - kaolin consumption) Provocative motion caused hypothermia in rats. and specificity (eg. conditioned food aversion) (reviewed in [8]). During the initial (basal) thermogradient session, This differential action of anti-emetic drugs on there was no difference in basal core body temperature nausea and emesis in the clinic led to the realization that between animals exposed to provocative motion and there may be different pathways and control systems for controls. In all tested rats, rotation caused consistent falls nausea and vomiting [8]. Furthermore, it is now clear in the core body temperature (Fig. 2A). These falls became that the wealth of existing mechanistic knowledge on apparent within the first 5-7 min of rotation, and did not the neural mechanism of the vomiting reflex, with its circuitry located mainly in the brainstem [8, 10], is not directly applicable to nausea – a subjective experience A. Food consumption. B. Water consumption. N = 9 that presumably originates in some forebrain areas. (each group) Consequently, identification of the key transmitter systems and receptors involved in nausea perception is essential for the improved care of the cancer patients. Providing that major methodological obstacle for advancing in this field * * is lack of adequate animal models for studying nausea [11], development and validation of new potential physiological indices for such studies is of major importance. In humans, nausea is commonly associated with facial pallor, sweating and gastric awareness [8]. It is less known, but well documented that in humans nausea is also associated with profound disturbances in thermoregulation, Fig 1: Provocative motion substantially reduced including falls in the core body temperature, modified food consumption (A) but had no effect on water perception of the ambient temperature and preference consumption (B) in rats. Both food and water consumption for cooler environment [12-15]. It is currently unknown were determined in absolute values and as a percentage of body whether pro-emetic stimulation elicits similar disturbances weight. White bars - control group; grey bars - after provocative motion. * - significantly different from control (P<0.01). www.impactjournals.com/oncotarget 1566 Oncotarget reach steady state or reverse until rotation was terminated. motion, we observed rises in core body temperature Following return to the thermogradient, core body in rats returned to their home cages after the initial temperature returned to the basal level within 30 min. In thermogradient session. Their temperature started to fall contrast to hypothermic responses elicited by provocative after reaching peak, but slightly increased again following Fig 2: Provocative motion elicited hypothermic responses (A) and had no effect on the preference for the ambient temperature (B) in rats. Note that in control animal, moving them to home cage and back to the thermogradient setup provoked rises in body temperature. ** - different from basal values, p<0/01. Fig 3: Provocative motion causes rise in tail temperature indicative of vasodilatation. A - mean group data (n=7) from the experiment where either